Circuits mounted in computers, various mobile devices, and so forth include various kinds of many IC chips. The IC chip is largely classified into a controller or central processing unit corresponding to an upper level control device and a peripheral controlled by the controller or central processing unit, the peripheral operates with the control of the upper level control device, or serves to transfer control commands to lower level devices.
For this purpose, communication is performed between an upper control device and a peripheral, or a peripheral and a lower level device, and communication terminals are provided for communication therebetween. This communication can be utilized, for example, to control microprocessors, LCD driver chips, remote I/O ports, RAMs, EEPROMs, telephones, or video system modules by an upper control device.
RS232C and IIC (Inter IC Bus) methods are typically employed for the communication between chips or between modules. Besides, a linear step method employing the concept of PWM (Pulse Width Modulation) and a shift method employing a counter are also used for the above communication. The IIC method uses two pins to perform a communication; one for transferring data corresponding to control commands and the other for transferring clocks for synchronization. This IIC method enables high-speed communication approaching 100 Kbps and 400 Kbps. The counter method selects the predetermined number of commands according to a signal from a master side. For example, in the case that the counter method is set to be capable of controlling eight commands, eight commands are counted up in the order and a desired command is selected among eight commands.
These existing bus communication methods have many problems originating from the afore-mentioned properties. First of all, in the IIC method of enabling high-speed communication, two pin terminals should be prepared and thereby a bus should be also configured in two lines. Therefore, the IIC method makes it more difficult to make a circuit module smaller while allowing the circuit module to be more integrated. The shift method, which transfers data in a single wire method, is quire cumbersome in that sequential counting should be carried out to perform the eighth command after the first command. As a consequence, the shift method has problems in that the operation speed responding to a command is slow and it is difficult to indicate many operations and commands. In the method using a single wire, it has also been difficult to remove noises or request data again although the noises are added to signals in the middle of the transmission of the signals Hence, the existing single wire method has frequently suffered from the malfunction due to the noises.